When analyzing the transmission of electrical (including electromagnetic) power to a device or network, it is often necessary or desirable that the impedance of the device or network be known. In addition to the input impedance, however, various other input characteristics which also indicate how the device or network responds to the application of power thereto may be sought as well. Such other input characteristics are normally related to impedance in some way.
The reflection coefficient for a device under test provides a vector ratio between power reflected from the device under test and power incident upon the device under test. The more specific voltage reflection coefficient represents the vector ratio between the electric field reflected from the device under test relative to the electric field of the incident wave thereto. Both of these reflection coefficients related to a device under test are functions of impedance. For example, where a source of impedance Z.sub.I provides power along a uniform line to the device under test which has an impedance Z.sub.II, the voltage reflection coefficient is defined by the expression: EQU (Z.sub.II -Z.sub.I)/(Z.sub.II +Z.sub.I).
The standing wave ratio (SWR) is, in turn, a function of the reflection coefficient. That is, if a device under test has a reflection coefficient p, the SWR of a uniform transmission line is defined by the expression: EQU (1+p)/(1-p).
Accordingly, with the above sample definitions of the reflection coefficient and standing wave ratio, it is noted that these input characteristics are defined primarily by the input impedance of the device under test.
In reviewing technology pertaining to prior apparatus or method, it is recognized that prior technology does not teach the determining of input impedance of a device under test from power-related measurements made by the device under test itself. Similarly, no prior apparatus or method teaches the determining of other input characteristics--such as the reflection coefficient or standing wave ratio--from power-related measurements made by the device under test.
In order to determine the input impedance, reflection coefficient, or standing wave ratio of a device under test (apparently even those which make power-related measurements), prior technology has required separate measuring circuits to evaluate the input characteristics of the device under test.
Moreover, in prior techniques, the use of vector voltmeters, phase determining devices, and the like were employed when input characteristic determinations were sought.